1. The Field of the Invention
This invention relates to a membrane cartridge for use in reverse osmosis and ultrafiltration systems.
2. The Prior Art
My previous patent No. 3,417,870 describes a so-called spiral wound membrane cartridge typical of the prior art. The "module" of U.S. Pat. No. 3,417,870 is more aptly described, it is believed, in this application as a cartridge; and the backing material of U.S. Pat. No. 3,417,870 is referred to herein as a permeate transfer leaf.
As will be seen in U.S. Pat. No. 3,417,870, a product water or permeate transfer leaf overlays a central perforated collection tube, an end area and side band areas of the transfer leaf being attached to the collection tube surface by a sealing adhesive. Membrane leaves folded around separator leaves are arranged as shown between product water transfer leaves, end and side band areas of the membrane leaves being also sealingly attached to the product water transfer leaves. The assembly of membrane leaves, permeate transfer leaves and spacer leaves is tightly wrapped around the collector tube to form a spiral wound membrane cartridge.
The spiral wound cartridge design has worked well in reverse oxmosis and ultrafiltration systems and many commercial installations are now operating successfully. However, the application of sealing adhesive between the central collection tube and the permeate transfer leaf has often resulted in an imperfect seal in spite of most careful application techniques and selection of adhesive. The principal reasons for leaks appear to be the inherent difficulty of providing a glue that is compatible to use as a transfer leaf glue and still adhere well to the collection tube surface; and differential expansion and contraction between the glue at the collection tube surface and the collection tube itself. Such differential expansion and contraction may be due to thermal effects caused by temperature changes, and dimensional changes caused by increase or decrease in pressure. These effects, which may be encountered after glueing is complete, may break the seal between the transfer leaf and the collection tube surface causing a short circuit water leak at the collection tube surface. Testing after assembly has often disclosed from 20% to at times as high as 40% of assembled cartridges defective because of leaky permeate transfer leaf to collection tube surface seals.
A completely reliable and leak-proof seal between a permeate transfer leaf and the collection tube surface in a spiral wound membrane surface would be extremely advantageous.